specific for sulfhydryl groups and N-hydroxy-chloroacetylaminoarene substrates to identify amino acids that are crucial to the catalytic activity. the monoclonal antibodies will be used to help in establishing the areas of the molecule that are involved in catalysis. (3. Localize the acetyltransferase and mRNA in rat tissues by use of monoclonal antibodies and cDNA probes to identify those cells that may be at particular risk from these compounds. (4. Express acetyltransferase in bacterial and mammalian cells to verify the identity of the sequence and to provide a means by which cells can be provided with a metabolic activation system. (5. Compare the structures of acetyltransferases from other species that differ in their abilities to carry out N-,O- and N,O- acetyltransfer.